DLC deposition inside tubes using hollow cathode discharge plasma immersion ion implantation and deposition

Plasma immersion ion implantation and deposition into the inner wall of a small diameter tube has gained more interest. A custom-designed plasma source based on hollow cathode discharge excited by radio-frequency (RF) is utilized to deposit a DLC film inside the slender tube. The internal cathode nozzle (shielded by an external grounded electrode) is made of stainless steel 6 mm in inner diameter and, 10 mm in outer diameter whereas the inner diameter of the tube to be treated ranges from 20 to 40 mm. The discharge is ignited and sustained in tubes with inner diameter of 20 mm and lengths of 140 mm and 500 mm. The DLC films with similar Id/Ig value and G-band position can be fabricated on the inner wall of the entire tube. The film thickness increases from the bottom to the upper parts and the tube diameter also has a critical influence on the deposition rate and film thickness uniformity. This can be attributed to the special discharge behavior in the hybrid hardware system composed of the internal hollow cathode and tube itself. Better film thickness uniformity can be readily achieved by moving the tube. The custom-designed hollow cathode discharge system is demonstrated to be an effective tool to treat the inner wall of small diameter tubes.